Supercritical fluids have been known (Table 1) since Baron Cagniard de la Tour observed in 1822 that, above a certain temperature, a liquid can be converted to a gas without the appearance of a meniscus. In 1869, Andrews fully characterized the critical point in terms of critical temperature Tc and critical

Critical point Supercritical

Table 1 Advances in supercritical fluid chromatography

Cagniard de la Tour

Discovery of supercritical 1822



Characterization of


critical point

Hannay and Hogarth

Increased solubility


in supercritical fluids



SFC suggested



Demonstration of SFC


Giddings, Sie

Development of dense


and Rijnders

gas GC and SFC

Sie, van Beersum

FID used in SFC


and Rijnders

Sie and Rijnders

First use of term 'SFC'


UV/visible detector used


in SFC

Jentoft and Gouw

Pressure programming



Randall and Wahrhaftig

SFC coupled to mass



Novotny and Lee

Capillary column SFC



Commercial packed


column SFC

Commercial capillary


column SFC

pressure Pc. Hannay and Hogarth observed in 1879 that metal halides are soluble in ethanol above the critical point, and as early as 1897 Vuillard reviewed solubility in supercritical fluids. Isolated examples of the use of near-critical solvents for separation appeared between 1930 and 1960; more extensive applications, especially to natural products with the pharmacologically acceptable carbon dioxide have since appeared, based on extensive studies of solubility in supercritical solvents and on the properties of solutions. In parallel with SFC, analytical supercritical fluid extraction (SFE) has been extensively developed as a sample preparation technique.

The original idea for SFC was suggested by Lovelock at an international meeting in 1958, before Klesper, Corwin and Turner separated involatile porphyrins in 1962 using supercritical chlorofluoro-carbons at pressures up to 136 bar as mobile phase. In 1966, Sie and Rijnders developed both adsorption and partition chromatography using carbon dioxide, «-pentane and isopropanol at temperatures up to 245°C and pressures up to 80 bar.

The advantages of carbon dioxide as a mobile phase were quickly realised: it is an inexpensive material with good solvent properties, convenient Tc and Pc, non-combustible, easily delivered by pumping the liquid, and available in high purity. Although other compounds have since been employed as mobile phases (e.g. N2O, SF6, NH3, «-butane and «-pentane, xenon, and various fluorocarbons and chlorofluoro-carbons), CO2 has remained the most popular and widely used. Because of the variation of solubility with density and hence pressure, Rijnders suggested in 1967 that pressure programming in SFC should have a similar effect to temperature programming in GC.

In 1970, Jentoft and Gouw constructed a versatile high-resolution SFC chromatograph with a pressure-programming facility for packed columns up to 4-m long and «-pentane-methanol mobile phase for temperatures up to 215°C and pressures up to 650 bar; detection was by UV absorption. Styrene oligomers up to « = 32 could be analysed with this system. The affinities between GC with a dense gas as mobile phase and SFC were discussed and developed by Gid-dings between 1966 and 1969.

Novotny pointed out in 1971 the serious limitations in SFC of the pressure gradient generated by the column packing, and realized that SFC should be possible on capillary columns with a much smaller pressure drop. In 1981, Novotny and Lee demonstrated capillary column SFC equipment. Commercial equipment for packed column SFC became available in 1982, and for capillary SFC in 1986.

The 1980-90 period was one of rapid growth in the theory, instrumentation and applications of SFC. A multi-authored text edited by Lee and Markides appeared in 1990 summarizing the state of the art, and remains authoritative. Two series of international conferences on SFC and SFE, one based in USA and the other in Europe began in 1988 and continue.

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Solar Panel Basics

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